Kidney stones, which are also commonly known as urinary stones, are solid accumulations and aggregations of matter formed in the kidneys from minerals in the urine.
Urinary stones are typically classified by their location in the kidney, ureter, or bladder, or by their chemical composition. About 66% of those with kidney stones are men.
Kidney stones typically leave the body by passage in the urine stream, and many stones are formed and passed without causing symptoms. If stones grow to sufficient size (usually at least 3 millimeters (0.12 in)) they can cause obstruction of the ureter. Ureteral obstruction has many adverse side effects including discomfort, pain, and spasm of the ureter. In many cases, the pain is commonly felt in the flank (the area between the ribs and hip), lower abdomen, and groin (a condition called renal colic). In some instances, renal colic can be associated with nausea, vomiting, fever, blood in the urine, pus in the urine, and painful urination.
Currently, there are three primary treatment options that account for over 99% of the surgical treatments of kidney stones: 1) percutaneous nephrolithotomy (PNL), 2) shock wave lithotripsy (SWL), and 3) ureteroscopic stone removal (URS).
PNL is generally used for stones larger than about 20 mm in diameter, and is performed almost exclusively for large stones within the kidneys. SWL is generally used to treat moderate sized stones, for example, stones having diameters ranging from 5 to 20 mm. URS is commonly used for stones having diameters of less than 20 mm. While PNL is used exclusively in the kidneys, SWL and URS can be used to treat kidney stones in the kidney and the ureter.
In addition to the above techniques, medical expulsion therapy (MET) employs medications to assist in the natural passage of the stone. MET may improve the statistical likelihood of small stone (2-6 mm) passage provided the patient remains comfortable and stable. However, this may require days to weeks of observation in an outpatient mode, waiting with uncertainty for a stone to pass. In the event the stone fails to pass, the patient will often require an operative treatment using URS or SWL. To date, no medications exist to dissolve stones, and stones 7 mm diameter or greater have less than 10% chance of passage.
SWL and URS are both typically outpatient procedures, as opposed to PNL, which requires a hospitalization of 1-2 days after surgery. SWL is typically performed with intravenous sedation (no formal anesthesia) with no instrumentation inserted into the patient. However, success rates, defined as stone-free with a single treatment session, generally do not exceed 75%. SWL typically depends on the availability of an expensive mobile machine that is rarely hospital owned, traveling around on a scheduled circuit, typically once weekly for most hospitals.
In contrast, URS is performed in the hospital operating room almost always with general anesthesia. URS is normally available on a daily 24/7 basis, with the insertion of a small fiberoptic telescope into the patient through the natural urinary channels (no incisions). The telescope is advanced up the ureter to the stone, where, if small enough (2-5 mm), it may be extracted intact. Otherwise the stone is fragmented in place with a laser fiber passed through the telescope. Fragments are then irrigated out or extracted mechanically with miniature instruments. Success or stone free rates for URS are 95-98% in experienced hands.
Due to the outpatient scheduling requirement for SWL, patient selection must be limited to those whose pain is well controlled and who have no other relatively common co-existent emergent contraindications that a stone may present, such as infection or kidney failure. These complicating factors demand a more urgent intervention than SWL can provide.
Unfortunately, there are currently no surgical treatments that are available as an outpatient in the urologist's office. Each of the above techniques requires formal sedation or anesthesia and the support of in-hospital environment (URS) or mobile lithotripsy unit (SWL). Both of these treatments also require the use of radiologic support in the form of fluoroscopy to monitor the treatment and technical progress during the procedure.
The relative status quo of the above surgical techniques for urologic stone disease has been the case now for approximately 15 years in the U.S. There have been no significant technological changes in PNL or SWL technology in over 20 years and no new advances are advertised or anticipated from known current research efforts. The most recent innovations in the triad of stone surgery occurred with URS, with the introduction of the first miniaturized flexible ureteroscope around 1995.
However, current ureteroscopes generally include a requisite mechanical structure so that they can be actively steered and directed through the ureter to the location of the stone, and into the kidney where active steerability of the ureteroscope is mandatory. As a consequence, the sizes of these ureteroscopes have been limited to minimum diameters ranging from 2.5 to 3.0 mm diameter (7.5-9 F). Currently, no passively flexible exists exclusively for ureteral stone surgery.
Current ureteroscopes rely on the use of laser lithotripsy to destroy stones by passing a tiny laser fiber through a channel within the telescope. The laser fiber transmits laser energy from a separate laser source located in proximity to the surgical field. The laser fiber then is placed in contact with a stone under direct vision and the surgeon reduces the stone to dust and tiny passable fragments. The ureteroscope is removed and the patient awakens, goes to a recovery nursing unit and is discharged home. The sizes of current ureteroscopes are such that the technique of introduction and manipulation would not be tolerated by an un-anesthetized patient.
Accordingly, there still exists a need for devices and associated methods that can be used to remove urinary stones as a truly outpatient procedure that can be performed in a non-hospital, office environment.